Many heated vessels are employed in industry. Typical of such vessels are chemical reactors, electrostatic precipitators and the like. Such vessels are either themselves heated or contain materials which have been heated or which generate heat. If such a vessel must be heated, fuels such as oil, natural gas, coal and the like must be burned to supply the energy neded to heat this vessel. In the past, when fuels were far less expensive than currently, insulation of such vessels to retain heat supplied to the vessels was not necessary. However, with the ever-increasing fuel costs of today, and with the need to conserve fuel, it has become increasingly important to retain as much heat as possible within such vessels.
Even where such vessels need not be heated, such as in reaction vessels containing exothermic reactions and the like, increased emphasis on safety for plant employees dictates that protective insulation of these hot vessels be employed.
Thus, for whatever the economic or social reason, it has become increasingly popular, and is sometimes necessary, to insulate heated vessels. Numerous insulation panels have been developed to meet this need. Most of these panels have in common an outer surface panel, an insulation material and a means for fixing the panel structure to the walls of the vessel.
Most panel structures for heated vessels are fastened to the vessel by means of screws passing through the panel, the intermediate insulation material and into a girt fastened to the vessel. As insulation needs have increased, requiring thicker insulation batts, the fastening screws required have become longer and longer. Insulation thickness levels have now reached a point where fastening screws, such as stand-off screws, having the properties necessary for such an environment, notably being both self-tapping and penetration depth controlling, are unavailable or available only as a custom-made item, at great expense.
Even when proper fastening screws of the size necessary to fasten these panels to vessels can be obtained, problems do occur with their use. As temperature changes occur within the vessel, and thus throughout the panel structure, expansion and contraction of the panels, due to their thermal elasticity, occurs. When panels are fastened to the vessel and one another by means of screws passing through the panel structure and into the girt, shearing stresses are applied to the fasteners during such expansion and contraction, which shearing forces may eventually cause shearing and failure of the fastener.